1. Field of the Invention
The present invention relates to coding/decoding of 3-D mesh information, and more particularly, to a progressive coding/decoding method for 3-D mesh information which is used in the field of moving picture expert group (MPEG)-4 synthetic and natural hybrid coding (SNHC) and a virtual reality modeling language (VRML), and an apparatus thereof.
2. Description of the Related Art
Not only efficient coding of mesh data but also progressive reconstruction of transmitted mesh data is recognized as an important requisite for transmission of a 3-D object including 3-D mesh. When mesh data is damaged by a communications line error during transmission, part of the damaged mesh data can be reconstructed with already-transmitted mesh data by a progressive reconstruction technique. Thus, the amount of mesh data to be retransmitted is minimized. This progressive reconstruction technique is expected to be effectively used in future wireless communications or communications at a low transmission rate, since this technique has strong characteristics with respect to communications line errors.
FIG. 1 is a conceptual block diagram of a conventional 3-D mesh information coding/decoding apparatus. Referring to FIG. 1, a coding unit 101 is comprised of a connectivity information coder 102, a geometry information coder 103, and an entropy coder 104, and a decoding unit 112 is comprised of an entropy decoder 106, a connectivity information decoder 107, and a geometry information decoder 108.
A conventional method of compressing 3-D mesh data, which is used in MPEG, will now be described referring to FIG. 1. 3-D mesh data 100 input to the coding unit 101 includes connectivity information and geometry information, and the two types of information are coded respectively by the connectivity information coder 102 and the geometry information coder 103. Here, information 105 on a vertex structure is transmitted from the connectivity information coder 102 to the geometry information coder 103. Information compressed by the connectivity information coder 102 and the geometry information coder 103 is converted into a compressed bit stream 111 by the entropy coder 104.
The compressed bit stream 111 is input to the decoding unit 112 and decoded as follows. The compressed bit stream 111 is divided into connectivity information and geometry information via the entropy decoder 106, and the two types of information are decoded by the connectivity information decoder 107 and the geometry information decoder 108, respectively. Similar to the coding unit 101, information 109 on a vertex structure is transmitted from the connectivity information decoder 107 to the geometry information decoder 108. A reconstructed 3-D mesh 110 can be obtained by decoded connectivity information and decoded geometry information.
As shown in FIG. 1, a 3-D mesh is transmitted in the form of a compressed bit stream on a communications line. However, since the conventional method uses the entropy coder, it has poor resistance to transmission errors which may be generated in a communications line.
Since conventional coding with respect to 3-D mesh data is accomplished in units of the entire mesh data, it is almost impossible to perform partial reconstruction before the entire bit stream is transmitted upon transmission of coded data. Also, conventional 3-D mesh coding has an inefficiency problem in that even when a very small portion of data is damaged by an error of a communications line caused upon transmission, the entire mesh data must be transmitted again. For example, an encoding method (ISO/IEC JTC1/SC29/WG11 MPEG98/W2301, MPEG-4 SNHC Verification Model 9.0) proposed by the IBM company has been used for MPEG-4 SNHC 3-D mesh coding.